Concrete is one of the oldest known building materials. It is made from mixed aggregates, such as crushed rock or stone and sand, combined with cement and water. The components of concrete can be mixed in varying proportions which give concrete many different applications, for example, structural applications such as pavements and building panels to decorative applications.
Coarse aggregate, such as crushed rock or stone, forms up to 65% of the volume of concrete. The compressive strength of the aggregate is an important factor in the selection of aggregate for concrete. Specifically, it is essential that the aggregate has a high compressive strength and in particular, the aggregate must have a high compressive strength when wet. This is because concrete is made with water and preferably maintained wet during its curing. A low aggregate compressive strength when wet will lead to weakening of the concrete before the concrete has even set. Furthermore, most applications of concrete will result in the concrete getting wet, for example, buildings, pavements and bridges are all subject to rain. Therefore, using aggregate with a low compressive strength when wet will lead to weak concrete which will not be structurally sound.
Unfortunately, coarse aggregate for concrete is a diminishing resource and there is a large cost in terms of energy, financials and the environment in quarrying coarse aggregate suitable for concrete from the ground.
There therefore exists a need for alternative aggregates suitable for use in concrete, and compositions suitable for the production of aggregates. There is also a need for new types of geopolymers more generally, which can be used in a range of applications, including the formation of aggregate suitable for use in concrete, and the formation of entire structural elements from the geopolymer, including tiles, benchtops, and replacement pre-formed stone-like materials.
It has been proposed previously to produce new forms of concrete which contain a geopolymer binder in place of normal cement (such as Portland cement). Such concrete compositions additionally contain crushed rock and/or stone as the aggregate component, which is to be contrasted to the use of new geopolymer compositions for forming a substitute aggregate (stone-like) material itself. Geopolymer compositions have also been proposed for use as mortar pastes for gap filling, however such compositions do not contain the properties of the geopolymers described herein. Further, in the context of the preparation of geopolymer aggregate (stone-like) materials, such mortar paste compositions are distinctly different to the compositions, materials and methods that are the subject of the present application.